The present invention relates to a method of forming patterned coatings on substrates, especially electronic devices, by negative resist techniques. The method comprises applying a preceramic coating comprising hydrogen silsesquioxane resin and an initiator onto the substrate and then radiating a selected region of the coating for a time sufficient to cure the resin. The uncured coating is then rinsed away leaving the patterned coating.
Numerous photolithographic techniques are known in the electronics art. One such technique using "negative resists" or "negative photoresists" has become increasingly valuable as the size of electronic components has decreased. Basically, this technique involves 1) the deposition of a radiation sensitive coating onto a substrate, 2) selective radiation of the coating to cure it in certain areas, and 3) removing the uncured portion of the coating with a solvent. The resist portion which remains on the substrate is employed as a protective coating to permit further manipulation of the coated substrate such as selective etching, metallization, or any other treatment of the uncoated areas of the substrate. As such, the resist layer should be thermally stable and stable to any reactive etching. Moreover, the resist should be one which allows for good image resolution or discrimination such that extremely fine patterns can be created.
Cavezzan et al. in U.S. Pat. No. 4.939,065 describe materials which can be used as negative photoresists. They comprise organopolysiloxane polymers which can crosslink by hydrosilylation, a crosslinking catalyst, and a crosslinking inhibitor which is effective at ambient temperature but ineffective on exposure to UV radiation. The organopolysiloxanes described therein comprise an organopolysiloxane with a hydrocarbon group containing alkenyl unsaturation bonded to the silicon atom and an organohydropolysiloxane containing SiH bonds.
Similarly, Ito et al. in U.S. Pat. No. 4,826,943 describe negative resist materials consisting of polysilsesquioxanes of weight average molecular weight 2000 or more represented by the formula (CH.sub.2 .dbd.CHCH.sub.2 SiO.sub.3/2).sub.m (ClCH.sub.2 SiO.sub.3/2).sub.n, where m and n are molar percentages and total 100. These polymers are taught therein as being sensitive to radiation and resistant to oxygen plasma reactive ion etching.
Likewise, Babich et al. in U.S. Pat. No. 4,693,960 teach negative resist materials containing a polysiloxane with polymerizable ethylenically unsaturated groups and an acetophenone as a UV light sensitizer. These materials are taught therein to providing good resolution and resistance to oxygen plasma reactive ion etching.
The present inventors have now discovered that compositions comprising hydrogen silsesquioxane resin and an initiator are excellent negative resist materials.